TO THOSE who have followed politics for a dozen years or less, Thruston Morton, who died last Saturday, was not a household name: he retired from the Senate in 1968, at age 61, and did not hold major office in the three Republican administrations that followed. That was a pity, for the nation and for the Republican Party, because Mr. Morton, as much as anyone in his generation, symbolized a branch of the Republican Party that has played a constructive role in national and local politics but that seems, unfortunately, to be pretty much extinct today.

That branch of the party is defined not so much by an ideological label -- though people tended to call Mr. Morton a moderate or even liberal Republican -- as by its regional roots. Thruston Morton was a Louisville, Ky., Republican -- scion of the Ballard & Ballard Flour Milling family, chairman of the board of Churchill Downs, vice chairman of a Louisville bank. In politics, he was a Kentucky Republican, a descendant of that hardy breed that supported Mr. Lincoln's party in the Civil War and for years afterward. Kentucky Republicans had provided spirited and occasionally successful opposition to that state's rural-based Democrats since the 1860s, with strong support from independent mountaineers, blacks and Louisville city folks.

Thruston Morton, like other successful Kentucky Republicans, was a strong partisan -- strong enough to serve in the 1960 campaign as Republican national chairman (a position his brother, Rogers Morton, later held) -- but he dissented occasionally from conservative Republican orthodoxy on economic issues and was always a strong backer of civil rights. On foreign policy, Mr. Morton was an internationalist and served as assistant secretary of state in the Eisenhower administration; later he was one of those Republicans who had doubts about the wisdom of the Johnson administration's Vietnam War strategy.

Probably the most exhilarating moment in Thruston Morton's political career came in 1956, when he upset Sen. Earle Clements, the Senate majority whip, who was acting Senate majority leader following Lyndon Johnson's heart attack. It was a classic battle between a traditional Kentucky Democrat and a traditional Kentucky Republican, and Mr. Morton won with the support of many black voters. That began Mr. Morton's 12 years of service in the Senate, which ended only with his voluntary retirement. Since then, Republican administrations have followed policies and Republican campaigners have adopted strategies more attuned to the newly defined Sun Belt than to old-fashioned border states like Kentucky. But if Mr. Morton's particular kind of Republicanism has had few exemplars since his retirement, it is nonetheless an honorable tradition and one worth remembering.